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NITheP Seminar by Hilary Masenda "The search for dilute magnetic semiconductors and new directions"

University of the Witwatersrand
When Mar 02, 2018
from 11:30 AM to 12:30 PM
Where NITheP Seminar Room, 3rd Floor
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NITheP cordially invites you to a seminar by

Hilary Masenda

University of the Witwatersrand

Date: Friday, 2nd March 2018 Time: 11h30 -12h30 Venue: NITheP Seminar Room, 3rd Floor, H-Block

Title: The search for dilute magnetic semiconductors and new directions

Abstract: ZnO and GaN doped with 3d metals have attracted much attention since the theoretical prediction [ HYPERLINK \l "TDi00" 1 ] that wide band-gap materials are potential dilute magnetic semiconductors with high Curie temperatures (Tc 300 K), resulting from carrier mediated magnetic interactions due to itinerant holes coupling with localized dopant spins. This stirred investigations on the site occupancy and magnetic behaviour of Fe ions in metal oxides and III-nitrides using emission Mössbauer spectroscopy (eMS) following the implantation of radioactive Mn+ ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV γ-rays from the 57Fe Mössbauer state (populated from the 57Mn βdecay) reveal the majority of the Fe ions to have a 3d5 configuration in ZnO and the 2+ valence state located near substitutional and/or associated with vacancy type defects in nitrides2]}. eMS experiments conducted over a temperature range of 100-800 K show the presence of magnetically-split sextets in the “wings” of the spectra for ZnO, MgO, GaN, AlN [ HYPERLINK \l "HPG10" 3 , HYPERLINK \l "TEM101" 4 , HYPERLINK \l "Man15" 5 ]. The temperature dependence of the sextets in MgO and the nitrides relate these spectral features to paramagnetic Fe3+ (S=5/2) with rather slow spin-lattice relaxation rates which follow a T2 temperature dependence characteristic of a two-phonon Raman process while in ZnO the relaxation followed a T9 dependence. InN, however, did not show any magnetic structure in the spectra, suggesting the absence of high spin Fe3+ in the material. Further research on other active follow-up projects will be also discussed.

  1. [1]  Dietl, T. et al: Science, 287 (2000) 1019.

  2. [2]  Masenda, H. et al: J. Magn. Magn. Mater., 401 (2016) 1130.

  3. [3]  Gunnlaugsson, H. P., et al: Appl. Phys. Lett., 97 (2010) 142501.

  4. [4]  Mølholt, T. E. et al: Phys. Scr., T148 (2012) 014006.

  5. [5]  Mantovan, R. et al.: Adv. Electron. Mater., 1 (2015) 1400039.

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